ltmain: Use shared objects built in source tree

ltmain: Use shared objects built in source tree

It has been discovered that under certain conditions libtool creates
wrappers that prefer installed versions of the shared objects over
those built in the source tree. As a result, any tests run in the
source tree produce unreliable results.

* build-aux/ltmain.in: Alter to use shared objects in source tree
  instead of installed.
* Makefile.am: Added in tests/bug_71489.at.
* tests/bug_71489.at: Contains test case for bug 71489.